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Is it possible to determine if winds were high without groundspeed, wind speed, AoA or AoS?
I have a data set that includes TAS, IAS, GPS Lat/Lon, Inertial Lat/Lon, ENU speed,  inertial speeds, attitude, and accelerations. I don't need to know the exact wind speed, and I don't think that's even possible to calculate at this point, but I would like to determine whether or not wind speeds were significant at a certain point in the flight. Is this possible?

If you have TAS and ground speed (compute from GPS) you can get wind speed. If you have heading, you can also calculate direction. See this for more details.

@RonBeyer in other words, if I want to calculate ground speed, I can just take the GPS Lat/Lon and just take the distance that I travelled in the time of interest and divide that by the time, just as I would any other speed calculation?

But apparently you do have groundspeed -- is this what "inertial speed" means in this particular context?  If so, question could be edited to point that out (and title changed); if not, answer seems invalid.  P.S. -- it's may be worth pointing out that the earth-referenced frame is not the only valid inertial reference frame in some aviation questions, but if winds are variable, then it basically is.

In the inertial (Earth) frame, denoted by subscript $_E$, inertial velocity ($\bf{V^i}$) is related to air velocity ($\bf{V}$) and wind vector ($\bf{W}$) as follows:
$$\bf{W_E}=\bf{V}^i_E-\bf{V_E}$$
Air velocity is more commonly expressed in the body frame (subscript $_B$), and is related to the inertial frame via the rotation matrix, $\bf{L}_{BE}$, as a function of the Euler attitudes ($\phi,\theta,\psi$):
$$\bf{V_B}=\begin{bmatrix}u \\ v \\ w\end{bmatrix}=L_{BE} (\phi,\theta,\psi) \bf{V_E}$$
$\bf{V_E^i}$ can be transformed from the ENU velocity to NED, and you mentioned that attitudes are measured, so that leaves the air velocity components.
If you have AOA ($\alpha$), AOS ($\beta$) and TAS ($V_T$) measurements, they are related to the components as:
$$\alpha = \tan^{-1}\frac{w}{u}$$
$$\beta = \sin^{-1}\frac{v}{V_T}$$
$$V_T=\sqrt{u^2+v^2+w^2}$$
That's three equations with three unknowns. At this point, you have all the information necessary to solve for the wind vector.
Without AOA and AOS measurements, your only hope is to assume some reasonable values of AOA and AOS. For AOS, you can assume 0 if there is no lateral/directional input. For AOA, you may be able to use some offline data (e.g. wind tunnel, CFD) if your weight estimate and aerodynamic data are trustworthy.
An additional note, per your previous question on finding AOA and AOS without sensors, you have a real dilemma here: you cannot obtain both winds and flow angularities without sensors!


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Finding Angle of Attack/Angle of Sideslip using East/North/Up Coordinates
I've got a set of data that includes:

x rate, y rate, z rate (all ENU) which I'll call xd, yd, zd.
roll, pitch, yaw (which I'll call ϕ, θ, ψ)
roll rates, pitch rates, yaw rates

I'm looking at some math that is meant to convert these values to AoA and AoS, but I'm having trouble understanding exactly what's going on.
As far as I'm aware, this is basically just taking euler angles and making a rotation matrix and using that to find u,v,w. But I'm having trouble verifying the accuracy of this work (it was done by someone who is no longer with the program.)

xd, yd, zd are inertial speeds? How are you accounting for winds then?

@JZYL Yes, xd, yd and zd are inertial. And I'm not, I've only got so much data and I'm just curious as to roughly what values I'm looking at. I'll hopefully get some better data in the future.

You could implement a Kalman filter to estimate AoA and AoS, however, in addition to the inertial measurements you have, you would need ground and wind speed measurements. See for example:
Wenz, A., Johansen, T. A., & Cristofaro, A. (2016, June). Combining model-free and model-based angle of attack estimation for small fixed-wing UAVs using a standard sensor suite. In 2016 International Conference on Unmanned Aircraft Systems (ICUAS) (pp. 624-632).

What you've proposed is a reference frame translation of the aircraft velocity, so instead of the velocity referenced to East, North, and Up (ENU), it's referenced to the direction the aircraft is pointing.  That gives you components of aircraft velocity along the nose, across the wing, and towards the ground. (You can find more details on these conversions by Robert Stengel).  It seems like using velocity across the wing and along the nose you should be able to figure out sideslip, but this approximation only holds in situations where wind is much smaller than true airspeed.

You're assuming here that the motion of the aircraft relative to earth equals its motion through the air.  That means your equations may give an unusual angle of attack when there's simply an unusual vertical wind component, or may report the drift angle as the sideslip where there is no sideslip.  This assumption of zero wind may be valid for rough approximations or in cases of severely limited sensor suites like a low-cost UAV.  This approximation is especially good at high true airspeed, low wind, or if you only care about AOA and AOS derivatives (e.g. for yaw damper control).  However there are some cases where this approximation clearly isn't reliable:

Windshear can result in a dramatically higher angle of attack than expected
Gliders use warm rising air to ascend without the loss of energy that would be anticipated if you're looking at only velocity and pitch
Horizontal surface winds in many places are over 30 kts, and can be much more in the jet stream. (see a wind map for examples).  Many aircraft can land in over 10 knot crosswind component, which your formulas would estimate as a ~10 degree sideslip.

Non-negligible wind is the reason that other methods of estimating AOA are used in practice, such as model-based angle of attack using inertial measurements (sometimes called synthetic air data) is sometimes used instead.  This is the reverse of what you typically do in an aerodynamics course- instead of using known angle of attack and airspeed to find normal and longitudinal acceleration, you're using known accelerations to find angle of attack and airspeed. Ardupilot has an option to do this based on this paper by Joseph E. Zeis, Jr. Another potential alternative implemented by Tor A. Johansen, et al, in addition to inertial measurements, uses airspeed during turns to estimate the constant wind.
Keep in mind there aren't a lot of cheap AOA sensors for a reason besides manufacturing costs: angle of attack is important, but has limits on its practical applications as AOA cannot be considered in a vacuum.  It's usually more important to know your airspeed or acceleration. For example, at high speed if you attempt a high AOA maneuver, the aircraft will rapidly decelerate, and you'd have to lower the nose to prevent the AOA from going into a stall condition. Other limitations are described here.

AOA cannot be considered in a vacuum, indeed! :)

This was precisely the kind of answer I was hoping to get! I really appreciate it.
So, if I'm understanding correctly, the idea behind the "synthetic airdata" is to basically estimate the effect of the wind and apply that to the same type of calculation that I demonstrated above, obviously still resulting in an approximation of AoA/AoS, but a "better" approximation. You simply can't calculate AoA/AoS accurately without wind data. But in the case of a "low-wind" day, these kinds of calculations would give a moderately accurate (depending on your definition of those words) estimation.

@synchh I've added to my answer regarding synthetic air data: "This is the reverse of what you typically do in an aerodynamics course- instead of using known angle of attack and airspeed to find normal and longitudinal acceleration, you're using known accelerations to find angle of attack and airspeed.".  I've also clarified to answer your other question to indicate that I wouldn't say this is inaccurate, especially when wind is light and true airspeed is high, but like many approximations, you need to understand its limitations.

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What are some symptoms of a clogged fuel filter?
I can certainly imagine one of the symptoms could potentially be engine fuel starvation. If the fuel flow to the engine isn't totally blocked, how can one recognize a clogged fuel filter?

It sounds like you're asking in the context of a gasoline piston engine, but could you confirm?

The effect would almost certainly be similar to running lean - ie, if not enough fuel is making it to combustion your fuel to air ratio will be that of a lean mixture
Effects of lean mixture include

Overheating
Knocking sound when running, perhaps even popping/backfiring from exhaust
The RPM will "hunt", meaning it will increase/decrease attempting to find a stable RPM
Slow to pickup, ie when increasing throttle it will not change quickly RPM as it should

I had all these symptoms except for backfiring on my automotive engine when the filter was clogged.

It's pretty simple.  There will be no symptoms until the flow demand of the engine is more than the flow that can make it through the filter.
On a carbureted engine, as fuel in the bowl is consumed, the float valve will have to open more and more to supply enough fuel volume to keep the level in the bowl above the metering orifice or jet. Once the float valve is fully open and the flow is still insufficient, the level in the bowl will drop until the fuel metering jet starts to un-port; then the mixture leans out to the point where the engine starts to lose power from an over-lean mixture, then misfires and stumbles.  If you reduce throttle, it'll recover once the fuel flow from the system is more than what the engine is trying to use, and float bowl refills enough for the metering system to work again.
A similar thing happens when you restrict the flow to an injected engine, except that because the fuel distribution is fairly even, you tend to see just a power reduction from a lean mixture, then instead of stumbling and rough running, it just quits (like when you lean the mixture too much yourself).
It'll also happen sooner (less clogging) on an injected engine, since the injection system's metering equipment requires significant inlet pressure to work properly.  A carburetor needs less than 1 psi of fuel pressure at the carb to be able to keep the float bowl full (which is why gravity feed works fine with wing tanks, but if you have injection you have to have fuel pumps even with the fuel up in the wings) and so it can take a lot more flow restriction before the head of pressure at the carb drops to a critical point.
So the main symptom will come on when fuel demand is highest, on takeoff, and will show up as an unexplained power drop, possibly followed by stumbling and rough running, or just quitting, but when you ease up on the power, at some point it should come back.

Thanks! This was very helpful. So say I flew for 15 minutes and with no issue at a steady 1.5 gal/min (demanded and supplied), then throttled up a bit and my fuel flow demand of the engine was now 2.0 gal/min. If I throttled back down to a point where the engine required 1.5 gal/min, I then shouldn't be experiencing the same issues?

If there was a fuel flow restriction it should've shown up during the full throttle part during takeoff.  In any case, yes if you experience something, that goes away when you reduce power, there is likely a fuel flow issue and an obstruction could be a cause.  It could be other things, like an intake restriction; you never know.  A clogged filter is just a possibility, one of a bunch a things to be checked during troubleshooting.

The restriction would show up during take-off run if already there. If there is some debris in the tanks that clogs the filter during flight, it will show up during en-route climb—or at the worst possible moment if you need to go around.

Most significant symptom of a clogged fuel filter,  is reduced power at high power settings.  High power already taxes the filter's ability to flow fuel, with a higher flow.  Then demanding high flow will result in limiting fuel to flow through a lower limited capacity filter.  Sub par climb performance would be a good indicator.

Not many diesel aircraft engines -- not none, but your "such as accelerating while climbing a hill" makes me think you're not talking mainly about aviation...

@ZeissIkon good spotting - seems to be fixed now.  It is easy to temporarily forget which SE site you're on sometimes, mechanics/aviation does have areas of crossover.

Yep, piston engines have evolved along with both ground/water transport and aircraft.  Slower in aircraft, due to certification requirements, except during the major wars.

Without a cockpit indication (bypass light, annunciator, etc), then one has no way of knowing if a fuel filter is the problem, or if there is some other cause.  If one has insufficient fuel flow, then one has insufficient fuel flow; one can't fix the filter issue in flight, or address it other than perhaps to switch tanks, depending on the system, filter, and location.  If the immediate problem is stoppage of fuel flow or reduction to the point of partial power or loss of engine power, or surging, then whether it's a filter, pump, line leakage, fuel flow divider, etc, it doesn't really matter.  You can't trouble shoot those problems in flight.  Follow your procedures.  These may include using fuel boost, switching tanks, shutting down an engine, etc.
There are numerous problems that could replicate what one might see with a blocked fuel filter.  Unless a filter is entirely clogged with a contaminant, then reduced flow is the norm.  In some cases, flow improves, or engine performance improves, if power is reduced; debris drawn against filter media or the filter inlet may move or allow fuel passage with a reduced fuel draw.  Outside of that, changing fuel flow manually, follow the procedures and don't guess as to the cause.
On the ground, troubleshooting is another matter, and fuel flow may be measured across the filter, at injectors, at the carburetor inlet, etc.  Tanks may be inspected, filters opened or flushed or back flushed, etc, to check for contamination.
Look closely at what's recently happened.  Did you just switch fuel tanks?  Perhaps you have contaminated fuel.  Perhaps debris was behind the fuel selector, and admitted downstream by moving the selector.  Perhaps the selector has failed in a partial position.  I've seen all those happen, as well as ice crystals in fuel, algae, and debris in tanks.  Leaking fuel fittings, failed fuel flow divider diaphrams, incorrect fittings, old fuel lines in certain cases, and other factors have lead to problems which could just as easily be interpreted in flight as a filter problem...but you have no way of knowing without a cockpit indication.  Likewise, an obstructed fuel tank vent might lead to similar problems and might manifest itself similar to what might occur with a plugged or obstructed filter, including smoother engine operation at reduced power.  In any case, it's a good time to be on the ground wishing you were in the air, than the other way around.

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Why don't private jets use higher bypass turbofans?
Common private jet engines such as the Williams FJ44 has a bypass ratio of just 2.8:1. Installation requirements aside. From an engineering perspective is there much to gain in efficiency by going to a higher bypass ratio on such small engines?

I guess private jets doesn't fly that much to justify the increased cost with fuel savings, especially in a segment so far away from "economy".

Lower bypass ratios are more efficient above 45000 ft where most bizjets are designed to cruise.


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What integration of aircraft propulsion would be more efficient at sea level high speed flight? A turbofan, unducted fan or a turbojet?
For educational purposes I am designing a small single seat twin engine aircraft that will be as efficient as possible at sea level and at a variety of speeds 150-500+ mph. The goal is to be able to travel long distances at high speed while offering great acceleration and loiter characteristics.
All of the information I've found is regarding cruising altitudes where at speeds of 400mph or less the turboprop is more efficient then a turbofan.

The chart below shows the results at altitude.
My top two choices are a variable pitch unducted fan or a high bypass turbofan. Both would be mounted in the wing with unducted unit having the blades aft of the wing. Both could possibly include afterburner for accelerating to top speed.
None of these charts take into account the drag of the different sized engines and their respective arrangements. The TSFC is usually quoted at design intention or static thrust and not sea level at high airspeeds so it's hard to compare known engines.
The turbofan aircraft could likely be designed quite a bit differently as you could use thrust vectoring and a variable nozzle reducing the number of necessary control surfaces and therefore drag which is extremely important in the thicker atmosphere.

For unbeatable fuel economy and high speed, you can't beat a turbo-compound piston radial like a Wright R-3350.  The specific fuel consumption is down around modern car levels; maybe 2/3rds of a turboprop of the same HP.  Unfortunately, you have to live with vibration, oil leaks, maybe reliability issues... but who can't fall in love with the sound.

With regards to @JohnK 's comment, does your concept have to have a turbine engine? If not, would you accept experimental stage engines? Also, your specified speed range is quite broad...

@jpe61 It is only turbine engines I am considering at the moment. It needs to be smooth and reliable, like a gas turbine.

Thing with turbines is, that they are not optimal at lower altitudes (warmer air).  A wild thought: usa a propfan with afterburner ;)

Jpe61 From my understanding the propulsive efficiency is much higher at lower altitudes due to the thicker air offering better compression and also mass flow for the fan. I believe the temperature differential itself only has few percentage points of efficiency to offer.  It's the fact that there is less drag at altitude that offers much better overall efficiency. Also I suggested an after burning propfan in my question.

I was trying to find an article about propfan efficiency I've read, since I recall a propfan fitting your specs quite nicely. I'm sure you have read more on propfans than just the Wikipedia article? Roughly speaking a propfan would combine some of the best aspects of turbofan and turboprop in a way that would be beneficial for your project.
However, during my (so far unsuccessful search) I stumbled upon this: multiple purpose subsonic naval aircraft (mpsna) multiple application propfan ... (pdf), at a fast glance this seemed interesting and some of the mission profile kinda matches yours, right? Comparisons between propfan and turbofan start at page 138.
It is an old paper, but check it out.

Penguin ancestors took to the sea for food, not to set speed records.  There is absolutely no reason to design an aircraft to cruise at sea level.  Plus you take away a very important lifesaver in the event of engine failure, the glide.  Far better to fly in thinner air, where true airspeed can be pushed all the way to your Mach limit while the indicated airspeed is far lower.
Simply apply your graphs to higher altitudes for greatest efficiency, and, unless you plan to go over 400 knots, the turboprop should be your choice, unless you find a good mechanic for your turbo-compound radial.
The weather is also a bit smoother up there too.

"There is absolutely no reason to design an aircraft to cruise at sea level". Correct. I never stated it would "cruise" at sea level. It isn't an airliner. By long range I meant maybe 200 miles.

@usernamechecksout your graph is excellent.  You would do well to study the strategies of airliners, as they are obsessed with fuel economy.  It's all about the airspeed, until you go so high Mach number limits your speed (unless you go supersonic).  The higher you go, the greater true airspeed (TAS) is.  Another path to efficiency is minimizing drag.  A third, that even major names have been very slow to espouse, is cheaper fuel. CNG or LNG is 1/3 the cost of aviation fuel.  You're on the right track, go with the unducted fan (propeller).

That's wrong.  It may be more efficient to fly at 35,000 feet, but you don't find a lot of submarines at that altitude.

@Harper - Reinstate Monica actually you do, except their hulls have lower pressure out side and the bow planes are slightly larger.  I once thought a panic stricken Navy put rockets on the Sea View (VTTBOTS) in an attempt to keep up, then realized their minisub wasn't half bad.


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What is the fan pressure ratio in a turbofan?
What is it and how does it affect efficiency and thrust?

According to thefreedictionary.com, it is The ratio of the fan discharge pressure to the fan inlet pressure. Not sure if this is in the correct context.

I’m not convinced mixing of the flows at the exhaust is the main reason for selection of fpr. After reading the paper it mainly seems as a supercharging stage for the compressors. Fighter jet engines have around 30:1 and a fpr of 2 should double that. If you look at a lot of modern commercial turbofans the exhaust is so far from the nacelle both streams should easily be ambient pressure by then.


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With supplemental oxygen, what altitude can a pilot safely operate at?
Will there be operating limitations regarding ascent or descent speed to avoid decompression sickness?
What altitude will require a pressure suit?

Are you asking from a regulation standpoint or from a medical standpoint? If this includes regulation, then you need to say for which country.

Unacclimatized human needs around 14–15 kPa partial pressure of oxygen to breathe. Since total pressure is 15 kPa around 45,000 ft altitude, pressure suit is needed above that.
Given that decompression sickness isn't a concern in diving to 10 m, which corresponds to full one atmosphere pressure difference, I don't think it's a concern for high altitude flying with supplemental oxygen.
I don't think anybody flies unpressurized above 20,000 ft these days—even fighters are pressurized to cabin altitude around 20,000 ft, largely to provide some air-flow for equipment cooling—but in WWII aircraft did sometimes fly at 30,000 ft with no pressurization and no pressure suits, just supplemental oxygen (and heated suits, because it's brutally cold up there). So that can certainly be done without significant problems.

1. Decompression Sickness
Altitude Decomression Sickness does occur. This article from the FAA has some interesting facts about it, when it occurs, and how to prevent it:

Altitude DCS became a commonly observed problem associated with high-altitude balloon and aircraft flights in the 1930s.
Though modern aircraft are safer and more reliable, occupants are.still subject to the stresses of high altitude flight—and the unique problems that go with these lofty heights. A century and one-half after the first DCS case was described, our understanding
of DCS has improved, and a body of knowledge has accumulated; however, this problem is far from being solved. Altitude DCS still represents a risk to the occupants of modern aircraft.

Factors inducing it, and of mitigating it, are (more details in the article):

Altitude. Below 18,000 ft there are no serious effects, 87% of cases occur above 25,000 ft. The higher the altitude, the higher the chance of being exposed to it.
Repetitive exposures.
Rate of ascent.
Time at altitude.
Body health.
Scuba diving before flying.

One interesting thing about breathing pure oxygen is that it prevents and/or mitigates the effects of Altitude DCS:

One of the most significant breakthroughs in altitude DCS research was the discovery that breathing 100% oxygen before exposure to a low barometric pressure (oxygen prebreathing), decreases the risk of developing altitude DCS.

2. Pressure suits
The pressure suits that fighter pilots wear are for preventing passing out due to high g-load. During high-g manoeuvring the blood tends to want to sink away from the brain, and the extra pressure around the legs prevents this from happening to an extent. The same suits are used in fighter simulators, to give the pilot some cue of high extended g-load, which is not really possible to reproduce with a motion system.

So - can a human continue to increase altitude while breathing oxygen until in outer space? Problem is, above the Armstrong limit the fluids of our body start to boil, and mainly boiling fluid lining the alveoli in the lungs would pose a problem, with death occurring in 60 - 90 seconds. So a full body pressurised suit is required above 19 km (82,000 ft).

Armstrong limit is where you need the pressure suit to be full body, but you need something well below that, because somewhere around 45,000–49,000 ft the pressure drops so much that even 100% oxygen is not enough to breathe. But you can start with just pressurized mask, then you need a suit (lungs are not designed for much overpressure, so better not risk it with mask overpressure more than a few kPa), but can have e.g. hands out… above Armstrong limit you definitely need fully enclosed.


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How much slipping and sliding go on during short final?
NOTE: This is not a question about coordinated flight in the pattern. There is no disagreement that hasty skids to turn the plane faster from base to final can and do kill. The question is about what happens once the plane is aligned on final and now continuous micro- and small-adjustments are necessary to precisely land the plane on the centerline.
While flying Condor the other day, I noticed that when I depend on automated turn coordination it is exceedingly difficult to align the (simulated) glider with the runway. The reason is readily apparent in that a typical glider has a bank rate of less than 30deg/sec, and thus bank corrections happen far too slowly to effectively steer the plane. The world is simply going by too fast for the slow rate to yield the precision required for landing. And from a theoretical controls perspective, this is a poorly damped oscillatory system, which are famous for being touchy to control.
And yet, when actually flying for real, a century of anemically maneuverable aircraft have demonstrated that high roll rate is not a requirement for safe landing. What then is going on?
I hypothesize that while on short final we use the rudder extensively for fine control, while keeping the wings appropriately level for the cross-wind conditions. In other words, we intentionally and unconsciously slip and slide the plane in small amounts, because coordinated turns in this phase of flight are slow and even dangerous.
However, this is merely an uninformed hypothesis, and there is certainly a large body of evidence which can definitely answer this one way or the other. In particular, this must be well understood for autolanding systems.
Can anyone point to studies which looked at the rudder movement on final approach vs. in standard flight?
P.S. Anecdotes are interesting, but I think these should be confined to the comment section. I think in order to really answer this question we need results from empirical studies.

Anecdotally, I (and I think most GA pilots) don't use coordinated turns on short final, mainly because of crosswinds.  Slips are also useful for losing a bit of airspeed, when you come in rather "hot" - as might be the case if you're sharing the runway with commercial jets.  Though the gliders I've flown have spoilers and single wheels, so slips seem less useful there.  Though trying to explain is rather like asking the centipede how it handles all those legs: I don't really think about it. https://en.wikipedia.org/wiki/The_Centipede%27s_Dilemma

It depends partially on technique, some use crossed controls for crosswind landings, others use crabbing.

Note that there is a real aircraft that relies on auto-coordination only and lacks separate rudder pedals, the ERCO Ercoupe. Quick search suggests it has a fairly high cross-wind limit of 25 knots too.

Fwiw, the A320 has auto-coordination all the way to the ground, and pilots use rudder only below 30' to decrab, no rudder on final app whatsoever. Don't think it makes the airbus any harder to control on approach than any other conventional  a/c

@Radu094 That's true for every aircraft with a yaw damper.

A bit to be said about the contribution of thrust to the lateral control of crab.  The B-52 just stays there, landing with nose pointing off center.  With a glider, one can de-crab at many points in the final.  Some may feel more comfortable to stay coordinated until just before touchdown.   Note the wing sweep of the "52" will couple in a bit of roll, even without ailerons.

Last week I took up a new glider student for a ride / informal instruction-- he had trouble holding heading-- I took the controls to figure out how I did it-- then I told him "for small corrections, it works well to just keep the wings level with ailerons and steer with the rudder.  For larger corrections, you'll need to make more coordinated inputs."  I can also also tell you that when flying a model airplane I typically don't even touch the rudder stick at all on final, unless I'm making a correction for a crosswind, in which case I typically hold a relatively constant rudder input

(ctd) in which case I typically hold a relatively constant rudder input to keep the nose on average parallel to the runway centerline, while steering with the ailerons to actually stay on the extended centerline.  In a full-scale airplane or glider, having the advantage of a ringside view of the situation, I'd be more actively working the rudders with every aileron input, to keep the longitudinal axis of the aircraft exactly parallel to the runway centerline, while adjusting my left-right "position" relative to the centerline with the ailerons.

So, your mileage may vary-- it depends on the specific situation-- but there definitely is some sideslip going on at times--

@quietflyer Your instructional comment "for small corrections, it works well to just keep the wings level with ailerons and steer with the rudder. For larger corrections, you'll need to make more coordinated inputs." sums up well my suspicion about our inputs on short final.

PS it's of some relevance to note that the model airplane in question-- as would be true of most model airplanes and most full-scale airplanes as well-- exhibited vastly less "adverse yaw" than any sailplane would.  So again-- your mileage may vary-- it depends on the specific situation, including the specific aircraft involved--

Related: https://aviation.stackexchange.com/questions/91403/viable-to-slip-onto-the-center-line

It is fine to slip and slide through a turn when you have enough altitude; doing so while being slow and close to the ground is much less advisable. Coordinating controls in turns is especially important when being slow and low.
The key to a good approach is space: Fly a large pattern so you have enough time to adjust heading and sink rate during the final. It is amazing how well the human mind can interpret small changes in the viewing angle - fly coordinated turns until your flight path is parallel to the runway and adjust flaps and flight speed so the glide path will intersect with the ground maybe 50 m (150 ft) ahead of the point where you intend to touch down. If you are too high, increase speed and shift that imaginary intersection closer to you, and vice versa. When all is adjusted, you should have used up maybe half of the final approach and can enjoy the nice, stabilized approach and prepare for the touchdown. Round out when maybe 3 m (10 ft) high and kick the rudder just when you think the wheel will touch the ground in order to align the fuselage with the direction of movement. Open the speed brakes fully only when the wheel has started rolling. This will produce a great landing.
Use side slipping if you are too high and make sure that your speed is at least 30% higher than stall speed. The direction of the sideslip should be with the nose pointing away from the crosswind so the misalignment between fuselage axis and glide path is small. If this produces a well stabilized approach, do as I said above and end the slip just before the beginning of the flare. But train sideslipping at altitude before doing this for real!
The scale of gusts gets smaller as you approach the ground, so the large ones which can shift the flight path and roll angle considerably should die down as the glider sinks lower. Also, gusts tend to cancel out over time, so you shouldn't be too upset about single ones. In gusty weather you need to fly your approach at higher speed so you have some margin against wind shear close to the ground. Because roll damping decreases and aileron authority increases with increasing speed, being thrown around by gusts indicates that your approach speed is too low.
The glider's inertia is already reason enough that you cannot fly in a coordinated way while being blown around by gusts, so short-term deviations of the yaw string can be disregarded. Your reactions, however, should be coordinated. When flying faster, adverse yaw is lower and it will be easier to keep the controls coordinated.
And if there are still gusts, a glider will find thermals and should not land yet.

This is great general advice, but once the plane is pretty-much aligned with the runway, and short-lived wind gusts push it around a meter to one side or the other of the centerline, I question if we are truly flying in a coordinated fashion or even if it makes sense to try. My instinct is that roll rate is far too slow to compensate for the quick lateral deviations caused by turbulence and gusts.

@KennSebesta Agreed, the answer needed improvement. I added a bit about gusts.

"And if there are still gusts, a glider will find thermals and should not land yet." @PeterKämpf, lol, yes! Still, what I'm missing in these answers is empirical data. What we've been taught is a simplified form of the reality, and the gist of my question is to get at the underlying data for this admittedly small edge case.

@KennSebesta  a planes response to a gust is dependent on its mass to side surface area.  The force of a gust will take time to build  up lateral velocity.  Keep in mind how strong the wing lift is, and how much horizontal force even a slight roll can generate.  Yes, a very light wing loaded plane will be a bit more "twitchy" in the wind, but "perfect" landings under those conditions should not be expected.

@RobertDiGiovanni Consider that the Schw. 1-36 has a published roll rate of 15 deg/sec. If a gust banked the plane 10 degrees to the side, which is not uncommon in rowdy conditions, then it would take almost a full second just to neutralize the turn. Then it would take another almost full second to bank 10 degrees opposite to start the correction. Then we add more time to end the correction, etc... We can see that the numbers add up quickly and unfavorably: a turbulent gust which banks the plane cannot be effectively rejected in under 2 seconds when flight is purely coordinated.

@KenSebesta bank does not equal turn, and frankly, using rudder will not make much difference in controlling a side gust.  Fast and accurate aileron input is what you want.  Remember also, dihedral is helping you here, in addition to "published roll rate".  use that wing, coordinate with rudder.  You get 5 degrees in 1/3 second!

@RobertDiGiovanni Bank and turn are related if we are coordinated. So if we hypothesize that we are always in coordinated flight, then when the gust banks the plane, if we are to rigidly follow the rule then we will find ourselves in a decaying coordinated turn to the side of the perturbation. I think from this alone we can quickly conclude that on short final, it is not ideal to maintain perfect coordinated flight. My question is to find data on to what extent it's ideal to deviate.

@KennSebesta you have opened a very interesting discussion.  It may be helpful to specify what aircraft you are referring to.  All turns low and slow are dangerous, coordinated turns are by far the safest.  You may be overestimating the effect of gusts, although  microbursts can overwhelm even the largest of aircraft.  Keep in mind the "side gust" will also affect the tail, pivoting the plane into the wind.  A pilot can feel the gust and react immediately.  Especially under power, a coordinated turn into the wind will hold course while the pilot evaluates.

@RobertDiGiovanni you make some excellent points there. I definitely hadn't considered how the tail tends to weathervane, helping reject lateral perturbations. I think we're all in agreement there are a lot of tiny factors which sum up to... something. Although it's not clear to me which way that something points so I'm left hoping for some data.

You could be drifting into dangerous territory (pun intended...hahahah). There should be NO slipping and sliding going on in any airplane or glider on final except for side slips induced on purpose to lose altitude, or for crosswind compensation during the landing flare.
All maneuvering turns in flight must be coordinated. Cross control or skidding maneuvers, close to the ground, except for deliberately induced side slips, invite a spin if the plane gets too slow and stalls.
The technique you are describing, in effect, consists of pointing the nose at the target (the runway) with rudder because it gets results faster.  This results in uncoordinated flight, and lots of people have died from spins originating from this habit.
Even in a glider with a ponderous roll rate, all maneuvering turns must be coordinated banked turns to make the necessary heading changes.  You have to think of it in terms of headings on final, and adjustments to headings when required.
Like gliders, large airliners have similarly ponderous roll rates and they make coordinated turns on final like all other airplanes. It takes a bit of patience. If you are drifting off track, you make a heading change, the normal way, with a coordinated turn to a new heading, then another coordinated turn to adjust as required. None of this pointing the nose with rudder stuff.
The thing is, in gliders, you often need large aggressive rudder inputs just ahead of the aileron input to get a coordinated turn in the first place, and that's fine, it's the way gliders have to be flown.  But the objective is still to keep the yaw string straight as possible while maneuvering.

This is the conventional wisdom, but I'd like to see data to back it up. It's important to note that I'm not asking about pattern maneuvers, but about maintaining the centerline on short final. A 2-33's roll rate is so slow that it's very very challenging to get it to turn quickly, but if I want to make a precise landing on the centerline I need rapid fine control. I suspect that we are doing lots of little skids to keep the nose aligned. Either way, there must be data out there...

See @quietflyer's anecdotal experience about "for small corrections, it works well to just keep the wings level with ailerons and steer with the rudder. For larger corrections, you'll need to make more coordinated inputs."

No no no no no no no.   You don't need studies - this is very basic airmanship.   Quiet Flyer is playing with fire.  You will never get me skidding the glider around the keep it lined up except in the last few feet.  It is very bad flying technique and applies to gliders and power planes.  If the string is pointing off to one side and you stall, it's going to roll off on you.  If you're side slipping to stay lined up, wing down and opposite rudder, that's fine if you ensure you have a speed and AOA margin.  But skidding around flat to keep lined up at 100 or 200 feet is asking for trouble.

I could not agree with you more that if your yaw string is clearly pointing toward uncoordinated flight then you are playing with fire. I think we are talking about very different magnitudes, though. I am not suggesting that we are unconsciously kicking the rudder back and forth, which is what I believe you are concerned about. Instead, I think that we might be using it in such a way that it is not simply a slave to the bank angle, perhaps similarly to how we lead in with the rudder to counteract adverse yaw. And if this is indeed occurring, it is subtle enough to only be clear in the data.

In a cross wind landing one can stay coordinated and crab their way down to the round/flare phase, but over the runway rudder and ailerons have specific purposes.
The rudder points the nose of the plane straight down the center line.  The ailerons are used for lateral control, banking into any crosswind component.
For example, a 5 degree roll in a Cessna 172 at 2000 lbs lift would produce sin 5 × 2000 = 174 lbs of side force!  So, even "ponderous" rolling is effective to hold track.
Interestingly, short final can also be flown this way, at a safe airspeed.
For example, approaching "cross controlled" in a 172 would be suicidal at 50 knots, but much safer at 65 knots.  Importantly, while on short final,  flying in a straight line, slipping is not nearly as dangerous as in a turn, where differences in wing tip speed can become critical.
Over the runway, basically one does what is needed to control the aircraft until it is down and stopped.  Effect of rudder will vary with different aircraft.  In a flaring 172, it does little more than yaw the nose back and forth without appreciably changing the fight path.
All uncoordinated manuevers should be thoroughly tested at altitude before use in a pattern.
Regarding "the world going by too fast for the slow rate to yield precision", this is definitely true for very light wing loads such as paper airplanes, models, and birds.  Here, the "tricks" of controlling side wind gusts can be seen in the common seagull:  high wing design with anhedralled wingtips and no vertical stabilzer.  This design automatically banks into the wind without excessive yawing.
Full scale aircraft are seen in all shapes and sizes because their much higher wing loading (or mass to surface area) creates a much slower acceleration from a side force, that is more easily controlled.


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What are the design considerations for variable-pitch folding-propellers?
Folding props are increasingly used on self-launch gliders in order to reduce drag. Here is an example of 1m dia. props from LZ Design's FES system:

For self-launch gliders, due to minimally-sized power plants the props are optimized for the safety-critical climb phase, leaving cruise performance as an afterthought.
At full-scale power levels, i.e. 10-30kW, how are design considerations different for folding props vs. standard fixed-root props?
In specific, could an existing folding propeller be retrofit by simply having a root which pivots, or would the already-structurally optimized root of a folding propeller make this unworkable?
[*] Examples at What are the advantages/disadvantages of a forward-folding propeller?

asking if something is "reasonable" is opinion based. You'd better ask how much complexity is would add (objective, easily related with costs), how much weight it would add (objective and easily related with performances) and/or how much it would improve efficiency (objective, easily related to performance). BTW, I fail to see why you want to optimize such propeller for cruise as gliders don't use it for cruise.

Usually, the propeller is retracted inside the fuselage so there is no need to fold the blades.

@ManuH, the picture you linked to is the pylon style of motorized glider. Another style uses the blades pictured above, which are 1m in dia. and manufactured by LZ Designs as part of their FES system. I also disagree that gliders don't cruise. There is a world of sustainers which serve only for cruise, being too weak to effectively climb. Typical cruise is for returning to the departure airport when there is no longer usable lift, however some pilots cruise in order to do a "soarfari".

I only saw that in RC models. In manned gliders, I already saw feather as the center of the propeller is far from the side. One exception I know is the Stemme S-10VT for which blades and only blades retracts inside the fuselage but don't fold

the cruise part to return home is marginal and not a normal case. The properler's main use is to climb, thus there is little incentive to optimize it for other phases as it can do the job even if not optimize for and this job is a marginal and not usual job.

Yes and no. Cruise can be a very important part of the flight, but climb performance is so marginal that there's no room for a middle-of-the road blade pitch. With all due respect, I think you might have a fundamental misunderstanding of how these modern gliders are flown. Electric motors have revolutionized the field and new bounds are being pushed.

I may indeed, But motorized flight is not soaring. You should expand the use you want to make with your folding prop in the question. Yet your question still asks for opinion ("is it reasonable"). You really should transform it in a more objective one.

I'm not sure if you're intentionally splitting hairs here. Motorized flight is what happens at the beginning (launch) and end (recovery). The alternative is to do an outlanding and either have to disassemble the glider in some farmer's field or send a tow plane to retrieve it. The  many hours and hundreds--  if not thousands-- of km flown in between the takeoff and recovery is soaring.

@KeenSebasta we should move to chat

Let us continue this discussion in chat.

@ZeissIkon I don't follow. Your original answer didn't attempt to address the aerodynamic question, and was predicated on a misunderstanding of real-world glider flight operations. If you don't understand the question, could you give me some feedback so that I can improve it?

Yes, although contest rules to date haven't yet motivated doing both at once.  In F1D international competition, propellers are commonly variable pitch (Indoor Model Airplanes: The Best of Indoor News and Views, ed. Tim Goldstein, pp. 138-144) to better exploit the gradually diminishing power during a flight, and sometimes variable diameter (ibid., pp. 119-126) to reduce drag like a folding propeller would.  Although not a contest winner, R/N Models' "Maverick" kit included a folding propeller purely for drag reduction.
No: if you need variable pitch for efficiency from a variable-power engine, and folding for drag reduction, it's simpler to reduce drag by feathering (changing pitch so far that the propeller won't windmill while unpowered) instead of by folding.
No, for a special case:  For propellers of the size you show, 8 to 16 inches diameter, 300 to 2500 watts electric power, a typical flight profile alternates full power climb with zero power glide (hopefully finding thermals to stay aloft).  Partial throttle only wastes energy.  Proving that mathematically is hard, but it has been verified with numerical simulation.  "Cruising" is best done with a burst of climb (what the propeller is best at) followed by a long glide (what the wing is best at).  At any rate, for a full on / full off power source, a single pitch is optimal.

Thanks for your thoughts and links. FYI, the pictured prop is 1m in diameter. The application is full-scale flight with 15-25kW of power, and so I wouldn't be surprised to learn that there's somewhat marginal utility in comparing to small scale model airplanes. For instance,  in 13.5m FES gliders the saw-tooth/dolphin approach to covering ground has proven to be less efficient then level cruise.

BTW, a feathered prop is very draggy, to the point of destroying the plane's ability to climb in anything other than strong thermals. Folded props do not suffer this pathology and have a minimal impact on drag of 5-10% overall.

Thanks for indicating the scale.  Sure, the rules are different there.  Particularly about feathered props:  that big, the nonzero pitch at each point along the blade results in essentially a speed brake, even though the pitches cancel out so the prop doesn't spin.

It is aerodynamically feasible, but it is not very practical.
Variable pitch is only worth the weight and complexity if the plane has a wide speed range, able to fly either very slowly or very fast, and needs to remain efficient throughout. If the speed range is not great then the aerodynamic benefits will be minimal and it is not worth doing.
Combining it with a folding prop poses no aerodynamic issues other than making the mechanism sufficiently compact to avoid unacceptable drag. But it does pose engineering ones; can a suitably compact mechanism be made strong, stiff, light and reliable enough for a realistic cost?

https://i.sstatic.net/VhG4q.jpg suggests that the efficient performance range for a pure climb prop is very narrow. It looks like even a 10 degree shift in pitch angle could increase range by 50%, which is substantial on a small battery pack. Do you think that this graph generally holds for all props, or is it only props designed with variable-pitch in mind which can have such a broad operation envelope?

The whole point of variable pitch is to broaden the operational envelope. I doubt that any graph holds for more than the prop it was measured on, especially when the design parameters and optimisations of fixed and varying pitch are so different.


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Under what legal standing can after-hours ground access to an airplane be forbidden? (USA-specific only)
This came up when a friend was unable to access his airplane because the security guard refused to open the gate. It was a mountain flight in a small plane, and so a timely departure was urgent for safety. The security guard didn't have a reason not to let the pilot access his plane, he simply felt he didn't have the authority to make that decision.
In the end, he was only delayed 45 minutes and didn't miss his weather window. But after I heard the story, it got me thinking what we should do when confronted with this situation, especially if the delay will cause severe consequences (missing a weather window, for instance).
In the US, under what normal conditions can a pilot be forbidden access to her/his plane, and what are the legal justifications for that? I have flown out of the obnoxious KBED and so am familiar with heavy-handed escorts, but this is different from arriving after-hours and being simply prevented from accessing your airplane. That would seem to run afoul of rules about private property, esp. since the tie-down is freely accessible if you fly in.
Generally, as a pilot I have always understood that I have the right to access any public airport for normal flight activities, baring some kind of NOTAM or other abnormal situation.
Are GA airports typically accessible 24/7? somewhat touches upon this subject, but it isn't well documented that these are "private (or state-owned) businesses". Indeed, airplanes and public airports are regulated by the FAA, and as such probably fall under all kinds of interstate commerce laws.

I could post the Michigan law which prohibits a person from entering or remaining on private property against the orders of the owner or the owner's representative. Would that be a satisfactory answer to your question?

Would that apply? The MI law likely requires some form of consent (implied or direct) as well as a direct order from the property owner. Moreover, I have to assume that the MI law makes specific reasonable allowances for retrieving personal property. Lastly, airport access is specialized, much like highway/bridge access. It's not private property when it's taxpayer funded. So limitations are acceptable but they have to reasonable, and they certainly can't wantonly endanger lives (which can occur with a delayed departure) or otherwise cause needless economic harm.

If you don't get a good answer here you could also ask on law.SE. They might be able to give a better answer on the legalities, I don't know how much this is really about aviation vs. general access to property.

Strictly speaking, it appears that they were not denying access to the aircraft, but to the airfield.  Presumably it has operating hours, like any other facility.  For a parallel, suppose that you had left your car in a parking garage, and wanted to get it after closing time?

This feels like it falls into the, "Timmy, you kicked the ball into mean old lady Hubbard's yard again!" territory. It's your ball/plane, but it's their yard/tarmac.

I’m voting to close this question because I believe it will get a better answer on law.SE

I feel sorry for airport security guards.  Do they all get entitled rich people accusing them of wantonly endangering lives when they're just doing what they were told to do, in order to make a living?

Private airports can do as they please, but airports that receive Airport Improvement Plan funding (i.e., nearly all public airports) are required to abide by the grant assurances, one of which is "Any proposal to temporarily close the airport for non-aeronautical purposes must first be approved by the Secretary." This is why your favorite airport, KBED, is open at night when they'd rather not be, and they have to resort to making operating there at night as annoying as possible instead.

As per my answer here the FAA does define "Public Airport" but does not specify that ground access must always be available. The answer mentioned in the question, you link here covers the general scenarios where issues could crop up:

Private Airports: Are generally free to make rules as they see fit and could potentially prevent you from entering the property even if the tie down they offer is free. There are lots private airports in the US and there are even some big airports that are privately owned. Private airports while conforming to certain federal aviation regulations may ultimately be built on private land which falls under different (often local) regulations.
Ports Of Entry: An airport that has customs facilities may prevent you from accessing your aircraft prior to clearing customs or if they have another reason not to let you onto the ramp. This can get tricky as its often administered by the TSA.
Local Regulations: Airports are often owned by local governments or port authorities there is nothing preventing them (as far as i know) from making a rule/regulation that prevented field access at certain times.

The most frustrating issue in my experience is the "Private FBO" problem. Often times airports are publicly owned but physical ramp access is handled by Private FBO's that may chose to not be open 24/7 or may (what sounds like in your case) station a clueless guard at the gate after hours. This creates more of a practical issue than a regulatory one, either the owning authority needs to mandate the FBO allow people onto the ramp at all hours or the FBO needs to step up their game a bit when it comes to educating their employees.
I'd say 8/10 times the gate code is the CTAF frequency...

This makes sense, but I'd like more meat to the property arguments. For instance, if a private landowner builds a road and connects it to the existing road network, and I drive onto that road, do they have any right to close the road behind me preventing me from leaving? This isn't at all clear to me. I definitely buy that they can impose certain reasonable constraints (e.g. "we have to meet you at the gate"), but they have to take into account my needs as well (since we both have private property at stake). In other words, they can't routinely enforce their schedule at the sake of mine.

I guess a follow-up, off-topic question is whether I'm entitled to climb a fence if I don't have the code for after-hours access. At my airport, the code is not CTAF, but it is written on the push-button to exit the ramp into the local diner's patio. So presumably all pilots who have arrived are allowed to exit after-hours. But if I didn't see the code/write it down on my way out, is the principle then that I am no longer entitled to access my private property after hours?

Private property rights vary by state which is why i left the answer broad. Just because something (a private service) is "connected" to a public network does not grant you blanket public use of it. If you drive onto a private road they can impose both reasonable and un-reasonable constraints since its private property. I think the answer is that broadly private airports on private property do not need to grant you access to your airplane if they chose not to (even though its your airplane).

Thanks for the thoughtful response. I see your point that the land is (potentially) private, but the airplane, being my private property, affords me equal protections under the law. So those rights collide in this context, and the solution isn't one-sided. Otherwise, the landowner becomes legally liable. FWIW, this is exactly what happens when sailplanes are forced to outland, such as on a farmer's property. The farmer can prevent the pilot from retrieving the plane on the pilot's schedule, but it then becomes the legal obligation of the farmer to fully and properly protect the asset.

One argument in the question and comment strikes me as odd. That is the assumption that public use of public, tax funded property can not be barred. Yet, this happens all of the time. You can not walk into a public building at any time of day or night. City hall, county courthouses, etc. are loosely, but securely, guarded. City and state parks can post hours of use and strictly enforce them. Even public roadways can be routinely closed or restricted without any accommodations to the public when need be. Why would an airport be different? We can count ourselves lucky for the access we have.

Now, it is unfortunate the OP had such an unpleasant and inconvenient customer service experience. But, it appears that it is more about convenience and not about rights. One solution to this situation is to see if the airport has keycards or other forms of access for resident aircraft owners. In my area, the only airports that do not have electronic or coded locks on one or more of the gates are the airports with fences low enough to step or jump (not climb) over. This is different than the faux security codes on self serve FBO doors. It is actually meant for residents only.

@DeanF., I feel you've mischaracterized my comments. In the case that the airport is 24/7 operational, but it's only barred to transient aircraft operators entering the premises, it becomes an issue of selectivity. That is not in itself wrong, but when gov't enforces selective restrictions there is always an accompanying justification (or else it wouldn't hold up in court). I agree with Pondlife that this might not be aviation specific and would be better asked in SE.Law.

If the airport is private property then of course they can bar you from entering. Just because you've left some property (a plane) there doesn't give you the right to enter whenever you feel. If I leave my jacket in your house that doesn't give me the right to force my way into your house to put it on.


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Best Practices when removing/inspecting/mounting control surfaces?
I am looking for a better way to essentially "mount" the control surfaces from a Boeing 737-747-777-787 and MD-11's. The current process is to just remove them and strap to a table. The issues with this is that it takes a lot of time to remove/inspect and possibly repair. the other issue as the way we are "mounting" them for said inspection. By strapping them to a table they can be bent, dropped, and it just isn't the best idea to have the control surfaces, like an 18 ft aileron, laying on a table...
I am just looking for any advice when it comes to mounting and servicing these parts as well as alternatives to strapping them to a table...

This is something you should talk to your Boeing service representative about.

Before you decide to change Boeing official procedures, you really ought to familiarize yourself with the reasons behind the crash of American 191.

The OEM will not provide any guidance for what to do with a control surface once removed, unless there is a Component Maintenance Manual produced by the OEM that may include instructions or specify a holding fixture for the component.

Your airline should have proper holding fixtures, basically a wheeled frame that mounts the surface at key attachment points, for control surfaces, either purchased from the manufacturer or designed in house.  The table strapping business is probably because the airline is too cheap to get the proper equipment.

The Aero MRO company I work for wants to come up with an in house design so we don't have to open a can of worms with Boeing. We have an inboard sling that is used to remove some of these controlled surfaces.

I was looking for some advice on handling these control surfaces without having to go to OEM. Although It seems like that's the best (safest) bet.

Well the basic advice for moving things around manually is to make sure you have enough people doing the moving.  Bad things happen when 2 guys try to move a surface around that should be handled by 4 or 6.  It can be done but it just takes more bodies and more planning and care.


text:
Why aren't "radioactive items" allowed on flights?
I've done physics, I completely understand what nuclear radiation is and why it is harmful. What I can't seem to figure out are the rules surrounding radioactive emitters/items on flights. Surely it's not just any radioactive items, because everything is at least slightly radioactive.
You get about 12 times the sieverts per hour at 35,000 feet than you generally do at sea level (3 μSv/hr in the air, 0.25 μSv/hr at sea level). And even then it's essentially harmless.
What if I had a strong radiation source, but encased in thick lead shielding? Or a strong emitter of only alpha particles? Do they measure it in Sieverts per hour, or Becquerels? Or Gray? All of it makes a difference.
Something that measures high in Gray or Becquerels could be damn near close to undetectable in Sieverts per hour - arguably the only relevant unit in terms of radiation effects on human health.
There's not enough info available to nerds like me, so insight would be greatly appreciated.

It messes with the x ray machines.

Radioactive materials, like several other hazardous materials, are allowed on cargo flights. I often handle radioactive packages. There’s a limit of 2 mSv/hr on the exterior surface, but the ones I handle are x-ray sources for testing welds, so they have to be very strong emitters on the inside. They are required to have labeling that includes a “cargo aircraft only” label. Even lithium batteries now must have a CAO label if not contained in a device. So it’s clearly for safety in case of an emergency

I'm quite curious. What are the forbidden items you are referring to? Some items brought back by tourists might be radioactive (e.g. rocks sample such as granite) and I doubt there radioactivity is measured before boarding.

@TomMcW: Lithium batteries not contained in a device are completely prohibited even on cargo aircraft; did you mean to say lithium-ion batteries?

@Sean We accept undamaged lithium metal batteries not contained in a device for transport. They must be shipped as hazmat and there are two labels required: a UN3090 label and a Cargo aircraft only label. The quantity is limited, but I’d have to ask my haz specialist what that is since I never pick those up, but I do sometimes deliver them. Usually it’s hearing aid batteries which are obviously very small.

Possibly related (though more confusing than helping): some planes use uranium as tail ballast, up to a ton of it per plane.

@RayButterworth Depleted Uranium?

Radioactive substances are potentially hazardous to people.
It is correct that many radioactive items would be perfectly safe to carry onboard, e.g. a key hanger with an alpha or beta particle emitter cast in acrylic, or a radioactive source for scientific purpose, if that source is properly packaged.

Glowing key hanger containing tritium. Image source: Nite GlowRing
Travelers usually do not carry radioactive items with them. If there is the need or wish to bring a radioactive item along, there is normally no need to have it in the hand luggage. This makes radioactive items different from lithium ion batteries. While potentially hazardous, there is a strong demand for lithium ion batteries on board. Banning them would essentially ban mobile phones and laptops.
Airport security staff as well as airline ground and cabin crew are neither qualified nor equipped to inspect and judge the safety of radioactive items. Opening the safe packaging of radioactive items might be dangerous. An item that cannot be opened cannot be checked if something else is hidden inside.
Finally, radioactivity stirs an irrational fear in many (if not most) people.
Given the need to restrict the transport of radioactive material somehow, and the difficulties in controlling it in a more sophisticated manner, the ban of such material from hand luggage seems comprehensible.


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Forward slip dynamics
I am perplexed on the dynamics of the forward slip. I am illustrating here:

The intended ground flight path is axis +y, and the plane is forward slipping by banking right + left rudder.
In order to keep being on the intended path, forces on x should add up to zero. However, the lift has a component to the right side (+x). I don't understand how the rudder is able to counteract this. The lift can be modeled as a linear force, thus acting on the plane's center of mass; instead, the rudder provides a torque that can change future geometry, but certainly not provide a linear force. What am I missing?

Do the answers here not explain it well enough?  https://aviation.stackexchange.com/questions/60774/what-is-the-difference-between-a-forward-slip-and-a-side-slip?rq=1

P.S.  lift would be on the Z axis of your diagram.

@MIchael Hall yeah, I've visited this before! But, while it clarifies between the two slips, it doesn't make me understand the dynamics. I've ignored the z axis, I have no problem there.

The Z component partly counteracts the weight, sure, I understand this. I am referring to the horizontal contribution of the lift due to banking.

Ok, I think I see your confusion.  Your arrows are wrong, the force generated by the rudder is opposite to the horizontal component of lift, not in the same direction as you depicted it.

Yes, I'm thinking how to correct this without messing up all the answers.

Answers are editable.  2.  It isn’t your responsibility to edit your question to match the answers that are given.  3.  If the light came on and you identified the problem, you can answer your own question explaining the confusion or error in your premise.  4.  I’d answer, but heading to work…. ;)

You are confusing some of the directions. For a forward slip in the +y direction, you have to bank left. The lift and rudder vector should both point in the opposite direction.
That would still leave a sideways component. However, the airframe will also generate some sideways lift! In fact, that is exactly the reason why you have to make some bank angle at all; if the airframe only resulted in drag, you could perform a forward slip wings level.

Yes, a right bank with full left rudder sounds like the plane may be upside down in the immediate future, and not happily slipping.

@tedioustortoise I'm confused by your comment. Sounds like you're just describing a forward slip, which doesn't result in being upside down?

" if the airframe only resulted in drag, you could perform a forward slip wings level.'-- almost but not quite.  You'd need a slight bank in the same direction as the deflected rudder, to neutralize the sideforce from the rudder itself.  I once tried to replicate this with a radio-controlled swept-wing flying-wing aircraft with no fuselage but it did have a very skinny tail boom with a big rudder at the end of it.  Wasn't able to consistently demonstrate the need to bank in same direction as rudder, need to repeat in calm air with stabilization, autopilot, etc, would be a fun project.

Crosswind landings using the "wing down" method in such an aircraft would be extremely "interesting".  You'd actually have to hold the downwind wing down.  A little hard to wrap your mind around that concept...  Or if you try the "kick out the crab, keeping wings level" method of crosswind landing-- if you make the "kick" too early and keep holding the rudder deflection till you touch down, you start accelerating (accumulating "drift") not in the downwind direction, but in the upwind direction!  There's a mind-bender for you--

@quietflyer Nice. Indeed hard to wrap your head around. Does that mean that with a large enough wing sweep and a small enough fuselage you could forward slip wings level after all :)

@Sanchises-- yes it seems there ought to be some amount of fuselage side area-- very small, but not completely negligible-- where a true wings-level sustained slip ought to be possible--

A "true" wings level slip isn't a slip.  Good point about vertical stabilizer roll torque, but the manuever is essentially a "frozen turn".  Wing prevents lateral acceleration and relative wind counterbalances yaw torque.  Switching from S turns to the forward slip on high approaches helped to understand it that way.

Think it through in steps.
When, say, right rudder is applied just wings level, what has happened is that the camber of the fin/rudder has increased and its chord line offset to the left, imparting a yaw torque that yaws the body until a new equilibrium is reached.
The angle of the fuselage to the airflow, that its static stability force wants to seek, its weathervaning trim angle you could say, is offset to the right.  The airplane yaws right and stabilizes at a new yaw trim angle of attack as long as the rudder is held.  It's  as if you bent the trailing edge of a barn weathervane and it now points into wind but with an offset.
At that new trim angle, the fuselage is operating at a lateral angle of attack, and the thrust line is also offset in the same direction.  The plane starts a flat turn from the lateral fuselage lift and offset thrust line (if there is power on). So I'm in a wings level skidding turn in the direction of the rudder application.
When I lower the wing the opposite direction, I introduce side slip forces that oppose the lateral forces induced by the yaw's lateral lift. At the right bank angle, the magnitude of the side slip forces precisely cancel out the lateral yaw and thrust (if there is any power on) forces, the net result on the body's mass is neutral, no turning occurs, and you are in a forward slip.

Give me a few months to process this :)

A highly imperfect analogy, but may help with the metal picture: you are driving on a giant table top of ice with studded tires where you drift or skid through turns with the ass end out.  The car skids around in an arc to the right say.  Then the driver moves a magic lever and somehow makes the tabletop tilt to the left.  The car now wants to slide downhill to the left, as its limited traction is slewing it around to the right.  If the driver gets the tilt angle just so, the left and right forces cancel each other out and the car goes straight, even though it's pointed to the right.

"A side slip is similar, but less rudder is applied relative to aileron, so that the side slip forces are stronger; there is a net surplus of side force in the direction of the slip,"-- I think this is incorrect.  A net surplus of side force would cause a net acceleration-- also known as a turn.  Complete with all the dynamics that go with turning-- heading change, etc.  Not sliding-- surplus force causing sliding is an Aristotelian concept, not a Newtonian one.  All forces must be balanced in both cases

(ctd), and the only difference between the two, is that "sideslip" is the term we prefer to use when the function of the slip is to exactly counteract the crosswind component and allow the aircraft heading to be parallel to the ground track so the wheels are aligned with the ground track for a nice landing, and "forward slip" is the term we prefer to use when there is a little or no crosswind and the nose is cocked to the side relative to the ground track (better not land that way!) and the main purpose of the slip is simply to increase drag (or to increase forward visibility.)

And what term to use when practicing 3000' in the air and we can't see the direction of the ground track anyway?  It's completely arbitrary, take your pick, or just call it a "slip".

@quietflyer  I use the term "sliding" as a short hand for lateral movement. A landing side slip is a lateral motion without the heading change, because the opposite rudder is preventing the fin from keeping the body aligned into the airflow. An airplane changes heading because the fin keeps the body aligned into the airflow as the flow becomes lateral due to bank. You are moving sideways, but still pointed down the runway, tracking with it because of the crosswind. If you take out the rudder input and hold the low wing, the fin will align the body with the offset flow and now you are turning.

Ok I see your point. I'm describing it from a ground reference perspective when actually they are the same maneuver.

First, we must realize the purpose of a forward slip is to increase drag, which allows the aircraft a greater angle of descent for a given airspeed.
This manuever serves the same purpose as dropping flaps to increase drag.
Importantly, ailerons are used to control lateral track, using the "slip" to counteract the tendency of the aircraft to fly in the direction it is pointed.
It is the horizontal component of lift, created by controlling bank angle with ailerons, that offsets forces in the opposite direction.
Because your aircraft has right rudder in, you must slip to the left.  The wing lift vector in the diagram, therefor, needs to be pointing in the opposite direction.
So, the change in relative wind when right rudder is applied stops the right yaw and tries to push the entire plane to the right.  The left force provided by the horizontal component of lift compensates for this.
Notice the wing is also pulling the plane in the y direction, but in a very draggy way.  Thus, the aircraft is (deliberately) uncoordinated.


text:
How many flying-wings have been certified for manufacture?
There are a number of flying wings which were certified airworthy and conducted test flights, but how many made it all the way to production certification (equivalent of a normal type certificate in the US)? I can think of only two examples, both in the military: the B-2 bomber and the F-117A.
Were there any others?

I've been wracking my brain and all I can think of are amateur builts. It's really not that good a configuration, best suited, if at all, to gliders. Because the packaging is all wrong for anything but a glider, or bomber with a concentrated payload. You need a fuselage to put stuff.  Once you have one, might as well put tail surfaces at the end and get better handling qualities.  You can make the wing super thick, and put crap in that, but it's like making a fuselage fly sideways, massive unnecessary frontal area. And that's why you don't see them much. It just doesn't work in the real world.

@JohnK that's exactly where I am on this question as well. There are a lot of cool prototypes out there, but of the thousands of planes which passed through certification, no matter how crazy the ideas behind it (looking at you, Aircoupe!), nor how low the bar is (or was), AFAICT not a one was a flying-wing.

Would the F-106 qualify? Or is this a tailless and not a flying wing airplane?

Are paragliders certified? As flying wings they likely out-number all other aircraft configurations.

@clivehooper good question, but almost certainly not because paragliders would be operating under Part 103. I would also say they are not flying wings per se, so much as weigh shift. A potentially controversial claim, I admit, but for the purposes of this question I want to focus on rigid flying wings controlled and flown through the same aerodynamic principles as other standard fixed wings.

If flexible wings count: Hanggliders exist in thousands and have reached a great variety of certified types.
But there are also rigid-wing, foot-launched flying wings: The Mitchell Wing and the Swift (an acronym for 'Swept Wing with Inboard Flap for Trim') both started as a hangglider but were subsequently developed into a range of ultralight airplanes, all type-certified flying wings (Mitchell Wing B-10, Mitchell Wing A-10 and T-10, Swift Lite, Swift PAS, P-Swift, Tandem Swift).
Over to the oldest flying wings: The Etrich-Wels designs flew before anyone could certify them, but J. W. Dunne in Great Britain got one of his flying wing designs certified as the first stable aircraft; however, only the Burgess-Dunne was manufactured in any quantity.
In the Twenties and Thirties more flying wings followed, but few reached certification. Of the range of "Storch" and "Delta" designs of Alexander Lippisch and the Pterodactyls of G. T. R. Hill, only the Delta III achieved formal certification, but no commercial success. At least, the Waterman Arrowbile was built 5 times, but I cannot find proof for formal certification.
With the insights from German research and the increased impetus of the Cold War, designs like the Vought F7U Cutlass, the Douglas F4D, the Convair F-102, F-106 and B-58, the Saab 35 and the Dassault Mirage III went into large-scale production but can be better described as tailless than as flying wings. Manoeuverability and trim changes for supersonic flight made adding a tail an attractive choice, as the development history of the Boeing X-32 shows. However, deltas make excellent supersonic designs, so at least the Concorde should make the list.
On the civilian side, Charles Fauvel designed a range of flying wing gliders, of which the AV.22, the AV.36 and the AV.45 went into production. Honorable mention should also go to the Marske Monarch or the Haig Minibat.

Really interesting, thanks. I wasn't aware that hanggliders were type-normal certified. I thought they were all either experimental or ultralight. Also, whoa, flying-wing biplane, cool!

Looking at some of the links, it looks like at least one might not have gone through certification, or the wiki link is wrong. The D.8 is listed as "Experimental", with only 4 prototypes having been manufactured.

Last comment: where would I look up the certifications for those planes? The wikipedia links don't give much, if any, insight into the certification. Several planes I had always thought were homebuilt only, such as all of Jim Markse's designs.

@KennSebesta Hanggliders are indeed not certified like commercial jets, but they are manufactured in series and sold which requires proper certification in their class. For the very early designs like the Dunne D.8 rsp. Burgess-Dunne there were no comparable regulations and pre-war production numbers were tiny (5 in the case of the Burgess-Dunne). The Marske Monarch and Haig Minibat are added as a honourable mention because all of them indeed were experimental, a way to circumvent the excessive product reliability risks at the time. I also didn't mention the Horten III, of which 19 were built

How much fuselage may a "tailless" (no horizontal stabilizer) have and still be a flying wing? The Messerschmitt Me 163 Komet was an aerodynamic success, if a somewhat lackluster weapon. More than 300 were built.

From Wikipedia article on the Me163: " On takeoff, one had to attain the speed at which the aerodynamic controls become effective—about 129 km/h (80 mph)—and that was always a critical factor." Wow!

Please add the Fauvel gliders to that short list. The AV.36 was built more than 100 times (compared to fewer than 20 of the Horten III) and is more of a flying wing than the 163 (which really is a tailless aircraft).


text:
Which time zone applies for annual maintenance?
(This question is silly, but fitting for the end of the month.)
When is the latest that a plane owner can legally fly a plane which is due for annual at the end of the month? Is it 23h59m UTC on the last day of the month, or is it time-zone dependent?

If it is 23h59m UTC, then have there been enforcement actions against people for flying out of annual, and yet still on the last calendar day of the month?

If it is time-zone dependent, is the originating or the destination time zone the relevant one? If I took off in EST at 11PM and landed 90 minutes later in CST, having crossed into the CST timezone before 11:59PM, would that be a legal flight? And what about the converse, where the flight starts in a western timezone but finishes after midnight in an eastern time zone?

If you get yourself into a situation where this answer matters, you’ve probably got bigger problems.

@757toga I'm not sure I understand what you're saying. The calendar month is the entire unit, so if the annual were done on Jan 1st it would not expire until Jan 31st of the following year. C.f. https://www.aopa.org/go-fly/aircraft-and-ownership/maintenance-and-inspections/aircraft-inspections#1 The question is about where Jan 31st is defined. Is it UTC or local?

@StephenS haha, yes! But it's fun to think about, and it seems like many aviation conversations we have at the local airport are about this kind of minutia or trivia.

@757toga very sensible approach.

I would have to say the time zone that applies is the time zone of the country where the aircraft is registered since they have jurisdiction over the aircraft and its maintenance unless those countries' regulations say otherwise.
For cases like the US, I would err on the side of caution; for GA pilots, apply the local timezone where the aircraft is and obtain a ferry permit to fly to the airport where the inspection will happen. If there is an incident, I don't want to fight with my insurance company over time zones.
For larger operators that fly across time zones regularly, 14 CFR 91.409(c)(2) excludes them from the annual 12 calendar-month inspections providing the aircraft are on an approved inspection program per section (e) of the FAR and paragraph (c)(3) also excluded aircraft from a 12 calendar-month inspection if they are under progressive inspection program as outlined in paragraph (d) of the FAR.
So, for owners that regularly fly across time zones where this would be a significant concern, the FARs give them options where they can make the time zone question moot. For everyone else, a better question would be, why are you flying that close to the end of your annual in the first place?


text:
What would generally be required to get an STC for swapping wing sections on a glider?
There are some neat gliders out there like the Pipistrel Sinus where the wing can be shortened/lengthened considerably by swapping out the outer wing panels.

If I wanted to do something similar and keep the glider's certification, i.e. not have it permanently be experimental, what would the FAA generally want to see? Since the plane has already received certification, it means that all flight safety and load limit tests are acceptable. If the new wing sections introduce no new controls, and the new Vne is less than or equal to the old Vne, then it would mean very little changes before/after aside from the percentage of loading on the inner section and the stall characteristics.
What's interesting here is that there are no airframe modifications required to swap out different wing sections. The operating equipment changes, i.e. different outboard wing sections, but that's it. Moreover, gliders have a special regulation which allows the pilot to assemble/disassemble wings as part of normal operation.
In my way of thinking, it would be as easy as showing the new wing section doesn't make for unsafe aerodynamics, that it's strong enough, and that the airplane has done the flight tests to show that it still handles within the required envelope. But that's way too easy, now isn't it?
What does the FAA want to see in these circumstances? Would an ultimate load test be required, or would only the new sections have to be tested to ultimate load (since we know the old sections already pass)?
(Obviously the right answer is to call the FSDO, but I'm more curious than serious.)


text:
Why did Pipistrel design the Sinus with core wing sections just at 40' instead of well under?
The Pipistrel Sinus has detachable wingtips and wing extensions.

However, they designed the plane with a wing core span at 39'11", just barely larger than a standard "40' door" (which is actually closer to 39', since the hangar structure itself eats into the 40' width).
As can be seen in the below video, it's just barely possible to fit it into a standard 40' hangar. But I don't think anyone would say it's practical, it's just that it's possible.

This wingspan has greatly limited the airplane's appeal in the US market, and this leaves me thinking that there is some crucially important physical or regulatory reason why Pipistrel didn't make the tips sections slightly longer so the core section could have been slightly smaller.
In contrast, the Phoenix LSA has designed their wings so that the core section is 35' wide, even though the full wingspan is only inches shorter than the Pipistrel Sinus:

What was worth trading off readily fitting in the vast majority of US hangars for an extra couple inches of core wing? Maybe Pipistrel doesn't consider the US as a likely motorglider market to begin with, and so they unapologetically optimized for their home market?
Update:
@StephenS points out that the official tip-less wingspan is 39'11", so technically 1" under the 40'. I stand corrected and have adjusted the question.

Pure speculation, so I will only add this as a comment. Probably the wingspan just ended up being impractically long to meet performance goals.

In SI-units: 41' = 12.5 m

41 ft x 0.3048 m/ft= 12.4968 m. Could it be that Pipistrel, a European manufacturer from Slovenia, designed it to be 12.5m for the European market?

@DeltaLima Absolutely, except they still would have known that there's a huge potential market in the US which they could go after, and by making it 12.5m instead of 12m large they +- shut themselves out of it. Since they went through a certification process, there's no fixing this in post, either. They've locked themselves into a potentially 40 year design choice, so you can bet they thought it through before committing.

"...you can bet they thought it through before committing."  Plenty of bets have been lost being overconfident about a company's market research!  ;)

Per the Pipistrel USA Sinus FLEX web site, the wingspan without tips is 39’11” to fit in standard 40’ US hangars.  After pulling it out of the hangar, you would likely attach the long tips, which aren’t intended to fit in any hangar.
Yes, it probably would have been better to make it fit in a 40’ hangar with short tips installed, but I suspect those were designed for ramp tiedown.  Or maybe it fits in slightly larger foreign hangars but by the time they realized the problem with US hangars, it was too late to change the wing design.
Unless there’s someone here on the Pipistrel design team, it’s unlikely you’ll get an authoritative answer:

That's a great data point, I had read somewhere it was 41' without tips but clearly that was wrong. As an aide, keep in mind that many-- perhaps most-- 40' T-hangars  do not have 40' doors. The hangars repeat every 40', which means that some small part of that, typically 4" on a side, is not available as it is used for the building structure. The upshot is that a 40' hangar is actually 39' and change. I have update my question to reflect this.


text:
What were the forces imparted by the chicken gun?
How hard does the chicken gun hit? Putting aside the apocryphal story of the British engineers who forget to defrost the chicken before firing it, what is the peak force the average chicken imparts?
(Of course this is a function of speed and impact site, I'm just looking for a data point or two.)

Wikipedia says 270kts typically.

@JohnK, I saw that, but the peak forces will be a function of how compliant the chicken is and the wikipedia article doesn't cover that.

According to the relevant rules (for example 14 CFR 25.571):

The airplane must be capable of successfully completing a flight during which likely structural damage occurs as a result of -

Impact with a 4-pound bird when the velocity of the airplane relative to the bird along the airplane's flight path is equal to Vc at sea level or 0.85Vc at 8,000 feet, whichever is more critical;

Note that in the calculation of the kinetic energy, the mass of the bird (4lb, 1.8kg) enters in the equation together with the designed cruising speed of the airplane Vc (and obviously not the bird's flying speed).
That value of kinetic energy should give you an idea of how piercing the impact can be. Translating the value of kinetic energy into a force is quite complicated since the force depends on the structural properties both of the bird and of the hit structure. That's why chicken guns are still in use despite the fancy simulation tools run during the design phase.
Just as example, this is how it looks like reality vs. simulation (all pictures from this paper):

Getting a ballpark estimate of the impact forces might be done using an energy approach with some simplification; we suppose that:

the airplane's structure deforms in a spring-like way; actually after the impact the structure remains deformed and it might even be broken, so it doesn't really behave like a spring;
the impacting body does not disintegrate i.e. its kinetic energy is all transferred in deformation of the spring; this is also not perfectly true.

We have:
$E_\mathrm{k}=\frac12 mV^2=E_\mathrm{e}=\frac12 kx^2$
$F=kx$
Where $k$ is the rigidity of the spring, $x$ its deformation and $F$ the force needed to deform it.
Equating and extracting $F$ we get:
$F=\frac{mV^2}{x}$
Let's substitute some numbers:

$m=1.8~\mathrm{kg}$
$V=100~\mathrm{m/s}$
$x=10~\mathrm{cm}=0.1~\mathrm{m}$

$F=180~\mathrm{kN}$

That's really interesting, but I need the force, not the pressure. (We're trying to determine the reaction forces on the wing/fuselage attachment anchors if a birdstrike on the wingtip occurs.) Through your answer, I found DTIC_ADA021142, which includes pressures vs distance, and therefore can integrate to get force. Any chance you could update your answer with data from that, so I can mark the answer as correct?

@KennSebesta: done.

Thinking of it as a spring is insightful. This works out to a 50000G deceleration, which leaves me awestruck, but that's the math. This makes me think that the chicken-gun test is inadequate to answer my question for the airplane design, since considering these astronomical forces it's much more likely that the LE of the wing will cleave the bird in two.

My next SE.Aviation question: "how much force does it take to chop a bird in half with a NACA 4-digit airfoil?"

Rewatched the MythBusters episode to get their speeds and data.  Now, it's time to do some math.
$m = \frac{4~\mathrm{lb}}{32.174~\mathrm{ft/s}^2} = 0.124~\mathrm{slug}$
$V = 140~\frac{\mathrm{mi}}{\mathrm{h}} = 205.3~\frac{\mathrm{ft}}{\mathrm{s}}$
$t = 0.007~\mathrm{s}$
In both cases, $a = V1/t = 29333~\mathrm{ft/s}^2$
Since $F_\mathrm{avg} = ma$, $F_\mathrm{avg} = 0.124~\mathrm{slug} \cdot 29333~\mathrm{ft/s}^2 = 3647~\mathrm{lb}$
Separately, if we consider the numbers in the wikipedia article you posted, $V = 350~\mathrm{mi/h} = 513~\mathrm{ft/s}$. If we assume the same rate of energy dissipation as the MythBusters test and a 4lb chicken, then:
$k_\mathrm{MB} = \frac{1}{2}mv^2 = \frac{1}{2}(0.124~\mathrm{slug}) \cdot (205.3~\mathrm{ft/s})^2 = 2613~\mathrm{ft}\cdot\mathrm{lb}$
$\frac{k_\mathrm{MB}}{t_\mathrm{MB}} = \frac{2613~\mathrm{ft}\cdot\mathrm{lb}}{0.007~\mathrm{s}} = 373,311~\mathrm{ft}\cdot\mathrm{lb/s}$
$k_\mathrm{wiki} = \frac{1}{2}(0.124~\mathrm{slug})(513~\mathrm{ft/s})^2 = 16316~\mathrm{ft}\cdot\mathrm{lb}$
$t_\mathrm{wiki} = \frac{k_\mathrm{wiki}}{\frac{k_\mathrm{MB}}{t_\mathrm{MB}}} = \frac{16316~\mathrm{ft}\cdot\mathrm{lb}}{373311~\mathrm{ft}\cdot\mathrm{lb/s}} = 0.043~\mathrm{s}$
Then, $a = V/t = \frac{513~\mathrm{ft/s}}{0.043~\mathrm{s}} = 11737~\mathrm{ft/s}^2$
and $F = ma = 0.124~\mathrm{slug} \cdot 11737~\mathrm{ft/s}^2 = 1455~\mathrm{lb}$
If instead we assume the deceleration time is constant:
$a_\mathrm{wiki} = \frac{513~\mathrm{ft/s}}{0.007~\mathrm{s}} = 73285~\mathrm{ft/s}^2$
$F_\mathrm{wiki} = 0.124~\mathrm{slug} \cdot 73285~\mathrm{ft/s}^2 = 9087~\mathrm{lb}$
And interestingly enough, based on the MythBusters' testing, a frozen and thawed chicken would impart the same force.

Re last sentence-- how could that be true?  Any way to explain a bit to give some insight on how that could be true?  Is the idea that with the frozen bird, the windshield shatters before the before the full force can be applied, somehow somewhat akin to the advantage of a bullet that "mushrooms" quickly rather than maintains original pointed shape for longer?  Just grasping at straws here, and curious, feel free to ignore, or respond/edit, as you see fit--

Force is a tricky metric when evaluating collisions. Assuming the entire chicken is eventually "absorbed" by the aircraft (all pieces of the chicken eventually come to rest in the aircraft's inertial reference frame), the total energy (mv^2/2) and momentum (mv) transferred are equal, since m and v are equal. But force is not. The thawed chicken deforms on impact, dramatically increasing the collision times and correspondingly decreasing the, let's say very casually, "average" instantaneous forces. Some energy is also dissipated internally via deformation heating, unlike the frozen chicken.

In this case, the force calculation results from the impact time (as we are calculating average force).  In the MythBusters test (S2E10), both chickens stopped against the steel plate in 0.007s from the same speed.  This would mean that the force applied by the plate to stop the chicken (and thus the force imparted by the chicken - Newton's 3rd law) would be the same for each test.

I haven't seen the MythBusters episode, but in general MythBusters did incredibly poor science. It was entertainment, not science (and I quite liked the show). Another factor to consider is the area over which force is applied: the thawed and deforming chicken will spread out the applied force over a larger area than the frozen one. That factor may be more important than the duration of impact.

@TypeIA You're now invoking pressure.  We can't calculate pressure without more information and data of our own.  Failure is a function of stress, which shares units with pressure, and the peak stresses will be lower in if the load is distributed over a larger area.  At the same time, the force applied by the chicken will still be the same for a given mass and acceleration, even if the area is different.  I also did my own math based on their data instead of just trusting specifically because it eliminates everything but their raw data, which is no different than googling

In the first 2 "Chicken Cannon" episodes, the Myth Busters massively missed the mark. The third episode with the layers of glass panes, they got it right. Shooting into an iron plate doesn't model a bird hitting a windshield well at all... a 4-pound water balloon dropped on you from 6 feet would hurt a little (and soak your clothes), while a 4-pound block of ice dropped from that height would cause real damage. Same deal with thawed vs frozen chickens.

@FlyJunior172: thanks for doing this. Could we ask for it to be done in metric, so a wider audience can review the math, and not trip up on lbf vs lbm problems?